EP3628758A1

EP3628758A1 - Textured surface for titanium parts

Info

Publication number: EP3628758A1
Application number: EP19196144.0A
Authority: EP
Inventors: James A. Curran; Sonja R. POSTAK; Todd S. Mintz
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2018-09-27
Filing date: 2019-09-09
Publication date: 2020-04-01
Also published as: CN110958800B; US10901458B2; CN110958800A; US11340652B2; US20210109568A1; CN110958791A; KR20200035861A; US20200107462A1; US20200103937A1; KR102294459B1; US11493957B2; CN110958791B

Abstract

This application relates to an enclosure for a portable electronic device. The enclosure includes a titanium substrate having a textured surface that includes randomly distributed peaks separated from each other by valleys, where tops of the peaks are separated from bottoms of the valleys by at least a minimum separation distance such that the textured surface is characterized as having an Sq (root mean square height) that is greater than 0.3 micrometers.

Description

FIELD

The described embodiments relate generally to techniques for etching a surface of a titanium substrate. More particularly, the described embodiments relate to systems and methods for achieving a matte surface finish for the titanium substrate.

BACKGROUND

Portable electronic devices can include various operational components (e.g., display, processor, antenna, etc.). Enclosures for these portable electronic devices can be formed of various metals (e.g., anodized aluminum, etc.) having a high amount of strength and stiffness to protect these operational components. Additionally, it is preferable to process these enclosures such as to impart these enclosures with an attractive surface finish. However, specific types of metals, although having a high amount of strength and stiffness, are also difficult to process to impart an attractive surface finish. Accordingly, there is a need to implement techniques for processing these specific types of metals.

SUMMARY

This paper describes various embodiments that relate generally to techniques for etching a surface of a titanium substrate. More particularly, the described embodiments relate to systems and methods for achieving a matte surface finish for the titanium substrate.
According to some embodiments, an enclosure for a portable electronic device is described. The enclosure includes a titanium substrate having a textured surface that includes randomly distributed peaks separated from each other by valleys, where tops of the peaks are separated from bottoms of the valleys by at least a minimum separation distance such that the textured surface is characterized as having an Sq (root mean square height) that is greater than 0.3 micrometers.
According to some embodiments, an enclosure for a portable electronic device is described. The enclosure includes a titanium substrate that includes an external textured surface having alternating peaks and valleys suitable for diffusely reflecting visible light that is incident at the external textured surface, where tops of the peaks are separated from bottoms of the valleys by at least a minimum depth such that the titanium substrate is imparted with a gloss value that is less than 2 gloss units as measured at 20 degrees relative to the external textured surface when the visible light is incident at the external textured surface.
According to some embodiments, a method for forming an enclosure for a portable electronic device, the enclosure including a metal substrate, is described. The method includes forming a metal oxide layer that overlays a surface of the metal substrate by exposing the metal substrate to an electrochemical oxidation process, where the surface of the metal substrate is roughened by the electrochemical oxidation process to form a texturized surface having alternating peaks and valleys, and removing the metal oxide layer by applying a stripping solution, thereby revealing the texturized surface of the metal substrate.
Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.
This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements.

FIG. 1 illustrates perspective views of various devices having surfaces that may be processed using the techniques described herein, in accordance with some embodiments.
FIGS. 2A - 2E illustrate cross - sectional views of a process for forming a texturized surface of a metal part, in accordance with some embodiments.
FIG. 3 illustrates a flowchart of a method for forming a texturized surface of a metal part, in accordance with some embodiments.
FIGS. 4A - 4B illustrate exemplary images of views of metal parts, in accordance with some embodiments.
FIGS. 5A - 5B illustrate exemplary electron microscope images of top views of metal parts and corresponding profile views, in accordance with some embodiments.
FIGS. 6A - 6D illustrate exemplary images of views of metal parts, in accordance with some embodiments.
FIGS. 7A - 7C illustrate exemplary images of views of metal parts indicating a relationship between processing time and extent of the texturized surface, in accordance with some embodiments.

Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings may be expanded or reduced to more clearly illustrate the embodiments of the present invention described herein.

DETAILED DESCRIPTION

Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting.
In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments.
Portable electronic devices can include various operational components (e.g., display, processor, antenna, etc.). Enclosures of these portable electronic devices are capable of protecting these operational components from physical damage, such as during a drop event. The enclosures may be formed of various metals, such as anodized aluminum, which has a high amount of strength and stiffness that is sufficient to protect these operational components. Additionally, the surface finishes of these enclosures should also be aesthetically attractive. Titanium and alloys thereof may be utilized to form the enclosures of portable electronic devices. Indeed, titanium is harder than anodized aluminum. However, this hardness also makes it very difficult to etch and/or chemically etch titanium. As a result, titanium is characterized as having a high gloss surface finish, which may be considered aesthetically unattractive.
The embodiments described herein set forth techniques for texturizing the surface of titanium, titanium alloys, and other anodizable, hard metals (e.g., hafnium, zirconium, etc.) such as to impart a low gloss, matte surface finish. In particular, an electrochemical oxidation process may be applied to a titanium substrate (and other anodizable, hard metals) to form a metal oxide layer. The electrochemical oxidation process may texturize a surface of the underlying titanium substrate such as to form alternating peaks and valleys. Thereafter, the metal oxide layer is stripped and separated from the underlying titanium substrate such as to reveal the texturized surface.
According to some embodiments, an enclosure for a portable electronic device is described. The enclosure includes a titanium substrate having a textured surface that includes randomly distributed peaks separated from each other by valleys, where tops of the peaks are separated from bottoms of the valleys by at least a minimum separation distance such that the textured surface is characterized as having an Sq (root mean square height) that is greater than 0.3 micrometers.
These and other embodiments are discussed below with reference to FIGS. 1 - 7. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting.
FIG. 1 illustrates various portable devices that may be processed using the techniques as described herein. The techniques as described herein can be used to process metallic surfaces (e.g., titanium substrate, titanium alloy substrate, etc.) of enclosures of portable electronic devices. FIG. 1 illustrates a smartphone 102, a tablet computer 104, a smartwatch 106, and a portable computer 108. It is well understood that the use of personally identifiable information that is capable of being transmitted, received, and/or managed by these portable electronic devices should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.
According to some embodiments, the metallic surfaces of the enclosures of portable electronic devices can refer to a metal substrate that is capable of being anodized. In some examples, the metal substrate can include a titanium substrate, a titanium alloy substrate, a hafnium substrate, a zirconium substrate, and the like. In particular, the metal substrate can refer to a titanium or titanium alloy substrate. Titanium and its alloys thereof are characterized as having a high specific strength and stiffness, which makes titanium an attractive choice for the enclosures of the exemplary portable electronic devices described herein. For example, titanium has a Vickers hardness number of ~ 350 HV1. Thus, titanium can function as a protective coating to protect internal operational components carried by the enclosures, for example, when these portable electronic devices are dropped, scratched, chipped, or abraded. However, due to this hardness, it is also difficult to polish and/or machine the surface of the titanium substrate using conventional techniques. Indeed, the relative hardness of titanium relative to other metals allows for only a limited amount of roughening using conventional techniques, thereby imparting a relatively high - gloss finish that is highly reflective and may be considered aesthetically unattractive for portable electronic devices. Furthermore, titanium is also highly resistant to many conventional chemical etchants and/or electrochemical surface texturing techniques. As a result, only a limited amount of roughening of the surface is possible, which leaves a relatively high - gloss finish.
Furthermore, it should be noted that bare titanium metal, in contrast to other durable finishes (e.g., anodized aluminum or DLC coated stainless steel, etc.) is electrically conductive. Indeed, titanium and alloys thereof may provide a desirable material choice for creating electrical contacts having excellent hardness and abrasion resistance, coupled with low contact resistance and high electrical conductivity. In some examples, the titanium and the alloys thereof described herein may be used for forming electrical contacts for ports, data connectors, and contacts.
FIGS. 2A - 2E illustrate cross - sectional views of a metal part undergoing a process for forming a texturized surface of the metal part, in accordance with some embodiments. FIG. 2A illustrates a metal part 200 prior to undergoing a process for forming the texturized surface. In some examples, the metal part 200 includes a metal substrate 202 that is capable of being anodized. The metal substrate 202 includes at least one of titanium, a titanium alloy, hafnium, niobium or tantalum. In some examples, the metal substrate 202 is a hard metal (e.g., Vickers hardness of 100 HV and greater).
In some embodiments, the metal substrate 202 has any thickness that is suitable for anodization, whereby the metal part 202 is exposed to an electrochemical oxidation process, as detailed with reference to FIG. 2B. In some embodiments, the metal part 200 has a near net shape of a final part, such as the enclosures of the portable electronic devices 102, 104, 106, and 108. In some examples, the external surface 204 is characterized as having a planar shape or a generally planar shape, as illustrated in FIG. 2A.
According to some embodiments, prior to the surface texturizing process, the metal substrate 202 may be subjected to a machining process in order to impart the metal substrate 202 with a final shape. Thereafter, the metal substrate 202 is wet - sanded to remove any machining marks in order to impart the external surface 204 with a fine, uniform, smooth finish. Thereafter, the external surface 204 may be optionally polished to achieve a uniform high gloss finish. In some examples, the gloss measurements of the external surface 204 subsequent to achieving the uniform high gloss finish is ∼ 1100 gloss value at 20° degrees, ∼ 520 gloss value at 60° degrees, and ∼ 120 gloss value at 85° degrees
According to some embodiments, prior to the surface texturizing process, the metal substrate 202 may be subjected to a blasting operation in order to achieve a uniform roughness for the external surface 204. In some examples, the blasting operation includes subjecting the external surface 204 with 45 - 90 micron spherical zirconia blast media at ∼ 0.15 MPa. As a result of the blasting operation, the external surface 204 has a relatively high gloss finish, such as ∼ 0.2 gloss value at 20° degrees, ∼ 4 gloss value at 60° degrees, and ∼ 9 gloss value at 85° degrees. It should be noted, as understood by one of ordinary skill in the art, these aforementioned gloss values are still relatively high and may not, therefore, be optimal for achieving a cosmetically attractive matte surface finish.
FIG. 2B illustrates an oxidized metal part 210 subsequent to undergoing an electrochemical oxidation process in order to roughen and/or texturize the external surface 204 of the metal substrate 202. In accordance with some embodiments, the metal substrate 202 is subject to a high voltage anodizing process also referred to as a plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO). As a result, a metal oxide layer 206 is formed from the metal substrate 202. The metal oxide layer 206 overlays the metal substrate 202. In some examples, the metal oxide layer 206 includes a combination of at least one of an oxide, phosphate, silicate, aluminate or titanate, vandate, tungstae or molybdate coating. In some examples, the metal oxide layer 206 has a thickness between about 1 µm to about 50 µm.
The electrochemical oxidation process employs higher electrical potential than anodization. During the electrochemical oxidation process, the metal substrate 202 is oxidized to form an oxide layer. Plasma discharge events occur throughout the oxide layer, which modifies the structure of the oxide layer, thereby forming the metal oxide layer 206. The metal oxide layer 206 is characterized as having a crystalline microstructure. Additionally, the metal oxide layer 206 may also be characterized as a dielectric.
As a result of the electrochemical oxidation process, the shape of the metal substrate 202 is roughened to form alternating peaks 214 and valleys 212 at the external surface 204. In some examples, the alternating peaks 214 and valleys 212 may be randomly distributed or evenly distributed from each other. For example, a masking process may be utilized to control where the alternating peaks 214 and valleys 212 are formed along the external surface 204 during the electrochemical oxidation process. In some examples, the alternating peaks 214 and valleys 212 define a ridge. The electrochemical oxidation process causes plasma discharge events at the micron - scale to form throughout the metal oxide layer 206 in proximity to the external surface 204. Each plasma discharge event roughens the external surface 204 in a controlled manner that results in fine - scale roughness of the external surface 204 that forms the alternating peaks 214 and valleys 212. As understood by one of ordinary skill in the art, the metal substrate 202 may be a hard, anodizable metal such as titanium or an alloy thereof. As a result, the alternating peaks 214 and valleys 212 illustrated in FIG. 2B are generally impossible to achieve using conventional machining and/or chemical etchant processes. Indeed, most machining operations are large - scale operations that at best, process a metal surface at a scale of tens of microns. However, the plasma discharge events cause formation of craters within the metal oxide layer 206 that that form the alternating peaks 214 and valleys 212 at the external surface 204 at the individual micron scale.
In some examples, a rough interface 208 is disposed between the metal oxide layer 206 and the metal substrate 202. In some examples, the rough interface 208 is characterized as having a surface that corresponds to the peaks 214 and valleys 212 of the metal substrate 202 as modified by the electrochemical oxidation process. According to some examples, the rough interface 208 has a surface roughness between about 1 µm to about 10 µm.
As illustrated in FIG. 2B, the metal oxide layer 206 is caused by the electrochemical oxidation process. In particular, the electrochemical oxidation process involves creating plasma discharge events that result in converting any metal oxide material formed by the oxidation process into a ceramic material having a crystalline structure. The ceramic material of the metal oxide layer 206 may be characterized as having an opaque color with a Vickers hardness value of about 400 HV - 1000 HV. While the metal oxide layer 206 may be of interest for surfaces of the portable electronic devices 102, 104, 106, 108, the metal oxide layer 206 may be characterized as brittle and susceptible abrasion, chipping, and staining. Furthermore, the resulting metal oxide layer 206 is generally limited in the range and control of colors that it may be dyed unlike other metals (e.g., anodized aluminum, etc.).
FIG. 2C illustrates a magnified cross - sectional view of the oxidized metal part 210 subsequent to undergoing an electrochemical oxidation process in order to roughen and/or texturize the external surface 204, as illustrated with reference to FIG. 2B in accordance with some embodiments. As illustrated in FIG. 2C, the alternating peaks 214 and valleys 212 may be randomly distributed from each other. The tops (Pt) of the peaks 214 may have varied heights, and the bottoms (V_b) of the valleys 212 may have varied depths that are formed as a result of the plasma discharge events. Each plasma discharge event roughens the external surface 204 of the metal substrate 202 in a controlled manner that results in fine - scale roughness of the external surface 204 that forms the alternating peaks 214 and valleys 212. As illustrated in FIG. 2C, the tops (Pt) of the peaks 214 and the bottoms (V_b) of the valleys 212 are characterized as having an amplitude range (X₁). In some examples, the amplitude range (X₁) is between about 3 µm to about 7 µm.
According to some examples, the tops (P_t) of the peaks 214 may be rounded (i.e., not pointed) caused by preferential anodization of the peaks 214 relative to the valleys 212 during the electrochemical oxidation process in conjunction with forming the metal oxide layer 206. As a result, on average, the vertical distance of the tops (P_t) of the peaks 214 relative to a reference line (Lr) may be greater than the vertical distance of the bottoms (V_b) of the valleys 212 relative to the reference line (Lr). In some examples, the reference line (Lr) may correspond to an average distance between the peaks 214 and the valleys 212.
As illustrated in FIG. 2C, the metal oxide layer 206 includes pore structures 216. The pore structures 216 are defined by the impact zones 218, and the impact zones 218 are generally elongated spherical shapes that extend through a portion of the metal oxide layer 206 and towards the metal substrate 202. In particular, the pore structures 216 have diameters between about 5 um - 10 µm. As a result, the metal oxide layer 206 of the oxidized metal part 210 has a surface roughness that is different from the rough interface 208. In contrast to the extremely uniform, conformal coatings associated with more conventional anodizing - where thickness is generally uniform across large areas of an external surface and porosity consists of uniformly distributed sub - micron scale, parallel columnar pores (e.g., on anodized aluminum), the impact zones 218 vary greatly in size and contribute to a relatively rough, random metal/oxide interface texture. In particular, the impact zones 218 are formed as a result of melted ceramic material. As used herein, the term elongated spherical shape may refer to an elongated shape having a greater height than width. Additionally, the elongated spherical shape has generally curved sides that bow outwards along the center of the elongated spherical shape. According to some examples, the impact zones 218 are characterized as having an amplitude range (X₂). In some examples, the amplitude range (X₂) is < 0.2 micrometers.
According to some examples, the metal oxide layer 206 has a ceramic finish and/or structure. In particular, the electrochemical oxidation process is a high - voltage anodization process that melts metal oxide material subsequently to the metal oxide material being formed. In some examples, the ceramic finish has a low gloss finish and is in muted black, brown, and/or grey colors.
FIG. 2D illustrates a cross - sectional view of a texturized metal part subsequent to applying a chemical stripping process, in accordance with some embodiments. As understood by one of ordinary skill in the art, the metal oxide layer 206 is formed from the metal substrate 202. As a result, the metal oxide layer 206 is securely adhered to the metal substrate 202, but the metal oxide layer 206 may be removed by the chemical stripping process. In accordance with some embodiments, the chemical stripping process includes exposing the oxidized metal part 210 to a stripping solution to form a texturized metal part 230. In particular, the stripping solution includes a hot sulfuric acid solution (70 - 90% concentration @ 70° C - 90° C) or a hot phosphoric acid solution (50% - 80% concentration @ 70° C - 90° C). In some examples, the stripping solution is applied for ∼ 5 - 15 minutes. As a result of the chemical stripping process, the metal oxide layer 206 is completely removed from the surface of the metal part 202 such as to reveal the alternating peaks 214 and valleys 212. The underlying surface finish of the texturized metal part 230 is unique to the electrochemical oxidation process (as described with reference to FIGS. 2B - 2C) and the chemical stripping process. In some examples, the alternating peaks 214 and valleys 212 of the texturized metal part 230 is characterized as a low gloss, matte surface finish that is ideal for enclosures for the portable electronic devices 102, 104, 106, 108.
Beneficially, because titanium or alloys thereof is generally resistant to chemical etching, exposure of the oxidized metal part 210 to the stripping solution has no appreciable impact on altering the characteristics of the alternating peaks 214 and valleys 212. In particular, the size, shape, distribution, and/or geometry of the peaks 214 and the valleys 212 is maintained subsequent to exposing the oxidized metal part 210 to the stripping solution. Additionally, the tops (P_t) of the peaks 214 and the bottoms (V_b) of the valleys 212 may also not be affected by the stripping solution. As would be understood to one of ordinary skill in the art, if other metals having less resistance to chemical etching (e.g., aluminum, stainless steel, etc.) were anodized to form the metal oxide layer, the surface of the underlying metal substrate would be dissolved by the subsequent stripping solution. For example, a textured surface finish of an aluminum substrate having peaks and valleys would be eroded by the stripping solution. If an aluminum substrate is exposed to the stripping solution, the resulting aluminum substrate has a high - gloss surface finish. According to some embodiments, the metal oxide layer 206 cannot be separated from the metal substrate 202 in a controlled manner.
According to some embodiments, ultrasonic agitation may be utilized while exposing the oxidized metal part 210 to the chemical stripping solution in order to uniformly remove oxide material from the surface of the metal substrate 202. Indeed, the ultrasonic agitation process may yield a more controlled, more uniform process for removing the metal oxide layer 206. According to some embodiments, the exposure of the oxidized metal part 210 to the chemical stripping solution may be characterized as a self- limiting process when the metal substrate 202 includes a hard, anodizable metal that is generally resistant to chemical etching. In other words, the chemical stripping process does not progress any further into eroding away the metal substrate 202 after stripping away the metal oxide layer 206.
According to some embodiments, the metal oxide layer 206 may also be removed with a mechanical stripping process, alone or in combination with the chemical stripping process described herein. For example, the metal oxide layer 206 may be exposed to a blasting process with iron or zirconia media. The blasting process progressively chips away at the metal oxide layer 206 due to the brittle nature of the metal oxide layer 206. Thereafter, brief immersion of the metal oxide layer 206 in one of the aforementioned chemical stripping solutions may remove any embedded material and clean the external surface such as to expose the underlying metal substrate 202 having alternating peaks 214 and valleys 212.
As illustrated in FIG. 2D, the alternating peaks 214 and valleys 212 are maintained subsequent to exposing the oxidized metal part 210 to the chemical stripping solution. The texturized metal part 230 includes tops (Pt) of the peaks 214 and bottoms (V_b) of the valleys 212 characterized as having an amplitude range (X₁) between about 3 µm to about 7 µm. As a result, the external surface 204 of the texturized metal part 230 is characterized as a generally uniform, matte surface finish. In some examples, the external surface 204 has a gloss value of x < 2 at 20° degrees, x < 5 at 60° degrees, and x < 10 at 85° degrees. As a result, when visible light is incident at the external surface 204, the external surface 204 diffusely reflects the visible light at substantially all angles of incidence. In some regards, the surface finish of the texturized metal part 230 is comparable to a surface finish of a blasted anodized aluminum part.
According to some embodiments, the texturized metal part 230 has a surface finish quantified as a "root mean square height" (S_q value) of the external surface 204. The S_q value represents a standard deviation of height relative to the tops (P_t) of the peaks 214 and bottoms (V_b) of the valleys 212 of the texturized metal part 230. In some examples, the S_q value represents a vertical scale of the roughness of the external surface 202. According to some examples, the external surface 204 is 1 µm > S_q > 0.3 µm. In some examples, the S_q value is between about 0.7 µm - 0.8 µm.
According to some embodiments, the texturized metal part 230 has a surface finish quantified as a "root mean square gradient" (S_dq value) of the external surface 204. The S_dq value is a surface texture parameter that correlates inversely with the reflectivity and gloss of a surface. In other words, the higher the S_dq value, the lower the gloss surface finish. In some examples, the S_dq value is about 0.4 µm. In some examples, the external surface 204 is 0.1 µm > S_dq > 0.5 µm.
According to some embodiments, the texturized metal part 230 has a surface finish quantified as a "auto - correlation length" (S_al value) of the external surface 204. The S_al value is a surface texture parameter that represents a lateral scale of the peaks 214 and the valleys 212. In some examples, the S_al value is 8 µm. It should be noted that the S_q, S_al, and the S_dq values of the surface finish of the texturized metal part 230 correspond closely to the surface finish of brushed aluminum (e.g., blasted with zirconia, etc.), as will be described in greater detail with reference to FIGS. 4 - 7.
FIG. 2E illustrates a cross - sectional view of a coated metal part subsequent to applying a coating process, in accordance with some embodiments. In accordance with some embodiments, a coated metal part 240 includes a coating 242 that overlays the alternating peaks 214 and valleys 212 of the metal substrate 202. The coating 242 may be applied with a physical vapor deposition (PVD) to impart a color (e.g., black, gold, etc.) to the texturized metal part 230. The coating 242 may increase the surface hardness for improved abrasion resistance. Additionally, the coating 242 may include a clear oxide or oleophobic coating to avoid fingerprint stains.
FIG. 3 illustrates a flowchart for a method for forming a texturized metal part, in accordance with some embodiments. In some examples, the texturized metal part - e.g., the texturized metal part 230 - corresponds to the metallic surfaces of any one of the portable electronic devices 102, 104 106, or 108 described herein. As illustrated in FIG. 3, the method 300 begins at step 302 where a metal substrate 202 (e.g., titanium or alloy thereof, etc.) is subject to a processing step. In some examples, the processing step includes blasting the external surface 204 of the metal substrate 202 to form a matte surface finish and/or polishing the external surface 204 to form a high - gloss surface finish. It should be noted that the matte surface finish is still relatively high in gloss and far from an optimal matte surface finish for a portable electronic device that is desired in the consumer electronics industry.
At step 304, a metal oxide layer 206 is formed over the surface of the metal substrate 202 by applying an electrochemical oxidation process (e.g., micro arc oxidation, etc.). In conjunction with performing the electrochemical oxidation process, the external surface 294 of the metal substrate 202 is roughened to form a texturized surface having alternating peaks 214 and valleys 212. According to some examples, the electrochemical oxidation process includes applying a high - voltage anodizing process to the metal oxide layer 206 that causes plasma discharge events. The plasma discharge events cause portions of the metal oxide layer 206 to melt, thereby resulting in a crystalline structure. The metal oxide layer 206 may have a Vickers Hardness value of about 400 HV - 1000 HV.
Subsequently, at step 306, the metal oxide layer 206 is removed and separated from the surface of the metal substrate 202. In particular, the metal oxide layer 206 is exposed to a chemical stripping solution (e.g., phosphoric acid, etc.) during a self- limiting removal process that is dependent upon the metal of the metal substrate 202 being resistant to chemical etching. The chemical stripping solution completely erodes away the metal oxide layer 206 but does not affect (i.e., erode) the alternating peaks 214 and valleys 212 of the metal substrate 202. By removing the metal oxide layer 206, the alternating peaks 214 and valleys 212 of the metal substrate 202 are exposed. In other words, the alternating peaks 214 and valleys 212 correspond to the external surface 204 of the metal substrate 202.
Thereafter, at step 308, a coating 242 may be optionally disposed over the alternating peaks 214 and valleys 212. The coating 242 may impart the metal substrate 202 with a non - transparent color. Additionally, the coating 242 may increase the hardness of the metal substrate 202.
FIGS. 4A - 4B illustrate top views of exemplary metal parts, in accordance with some embodiments. FIG. 4A illustrates a blasted metal part 400 that includes a titanium substrate 402. The titanium substrate 402 illustrated in FIG. 4A was processed by blasting an external surface of the titanium substrate 402 with zirconia blasting media. According to some examples, the zirconia blasting media is between about 45 - 90 µm in diameter. The zirconia blasting media is applied at ∼ 0.1 - ∼ 0.2 MPa (carrier air pressure). As a result, the zirconia blasting media causes divots 404 to form throughout the external surface of the titanium substrate 402, thereby imparting the titanium substrate 402 with a generally uniform surface roughness. However, the divots 404 are shallow and barely penetrate the external surface. Thus, the resulting surface of the titanium substrate 402 is a relatively high gloss finish with gloss values of ∼ 11 at 20° degrees, ∼ 60 at 60° degrees, and ∼ 65 at 85° degrees. Furthermore, the blasted metal part 400 has an (S_q) value of ∼ 0.2 µm and an (S_al) value of ∼ 9 µm. In other words, the resulting surface finish of the titanium substrate 402 nowhere near resembles a typical surface finish of a blasted aluminum part having typical gloss values of ∼ 0.2 at 20° degrees, ∼ 4 at 60° degrees, and ∼ 9 at 85° degrees. Accordingly, blasting a metal part (e.g., titanium, etc.) does not result in a surface finish that achieves a matte, diffuse appearance.
Contrarily, FIG. 4B illustrates a texturized metal part 410 that includes a texturized titanium substrate 412 processed using an electrochemical oxidation process that results in a texturized external surface. FIG. 4B illustrates a texturized titanium substrate 412 formed by using a high voltage anodizing process to form an overlying metal oxide layer - e.g., metal oxide layer 206 - that causes alternating peaks 414 and valleys 416 to randomly form throughout the external surface of the texturized titanium substrate 412. Thereafter, the metal oxide layer is removed by a chemical stripping process that exposes the alternating peaks 414 and valleys 416. The resulting surface of the texturized titanium substrate 412 is a relatively low gloss finish with gloss values of ∼ 0.2 at 20° degrees, ∼ 1.7 at 60° degrees, and ∼ 9 at 85° degrees. Furthermore, the surface finish of the texturized titanium substrate 412 offers diffuse, low gloss reflections at all angles of incidence of visible light. Furthermore, the texturized metal part 410 has an (S_q) value of ∼ 0.7 µm and an (S_al) value of ∼ 8 µm and an (Sdq) value of ∼ 0.4 µm.
FIGS. 5A - 5B illustrate exemplary electron microscope images of top views of metal parts and corresponding profile views, in accordance with some embodiments. FIG. 5A illustrates a blasted titanium substrate processed using a blasting process that includes blasting an external surface of the titanium substrate with zirconia blasting media (∼ 45 - 90 µm spheres). As illustrated in FIG. 5A, the surface topography of the blasted titanium substrate exhibits an absence of peaks and valleys greater than or equal to about 1.5 µm. Furthermore, the corresponding 2D profile of the surface topography illustrates an amplitude of less than 1.5 µm. The blasted titanium substrate has an (S_q) value of ∼ 0.2 µm and an (S_al) value of ∼ 9 µm.
FIG. 5B illustrates a texturized titanium substrate processed using an electrochemical oxidation process. As illustrated in FIG. 5B, the surface topography of the texturized titanium substrate exhibits peaks and valleys greater than 1.5 µm. Furthermore, the corresponding 2D profile of the surface topography illustrates an amplitude of greater than 2 µm. The texturized titanium substrate has an (S_q) value of ∼ 0.8 µm and an (S_al) value of ∼ 8 µm.
FIGS. 6A - 6D illustrate exemplary electron microscope images of top views of metal parts and corresponding magnified top views, in accordance with some embodiments. FIG. 6A illustrates a polished titanium part. According to some examples, the polished titanium part has an (S_q) value of ∼ 0.007 µm and an (S_dq) value of ∼ 0 µm. The resulting surface of the polished titanium part is a high gloss finish with gloss values of ∼ 1200 at 20° degrees and ∼ 552 at 60° degrees.
FIG. 6B illustrates a blasted titanium part. According to some examples, the blasted titanium part is formed by blasting an external surface of a titanium part with zirconia blasting media (∼ 45 - 90 µm spheres). According to some examples, the blasted titanium part has an (S_q) value of ∼ 0.215 µm and an (S_dq) value of ∼ 0.08 µm. The resulting surface of the blasted titanium part is a relatively high gloss finish with gloss values of ∼ 23 at 20° degrees and ∼ 93 at 60° degrees.
FIG. 6C illustrates a coated titanium part. According to some examples, the coated titanium part is processed by blasting a titanium part, and subsequently coating an external surface of the blasted titanium part with a physical vapor deposition (PVD) coating. According to some examples, the PVD coating imparts a color to the titanium part. According to some examples, the coated titanium part has an (S_q) value of ∼ 0.22 µm and an (S_al) value of ∼ 6.1 µm. The resulting surface of the coated titanium part is a relatively high gloss finish with gloss values of ∼ 7.1 at 20° degrees and ∼ 50 at 60° degrees.
FIG. 6D illustrates a texturized titanium part. According to some examples, the texturized titanium part is processed by forming a metal oxide layer over a titanium part via an electrochemical oxidation process, and subsequently removing the metal oxide layer. According to some examples, the texturized titanium part has an (S_q) value of ∼ 0.76 µm and an (S_al) value of ∼ 8 µm. The resulting surface of the texturized titanium part is a relatively matte, low gloss finish with gloss values of ∼ 1.7 at 20° degrees and ∼ 9.1 at 60° degrees.
In comparison, anodized aluminum has an (S_q) value of ∼ 0.70 um, an (S_al) value of ∼ 17 µm, and an (S_dq) value of ∼ 0.15 µm. Additionally, anodized aluminum has gloss values of ∼ 4.3 at 20° degrees and ∼ 9.2 at 60° degrees.
FIGS. 7A - 7C illustrate exemplary electron microscope images of top views of metal oxide layers of metal parts, in accordance with some embodiments. In particular, FIGS. 7A - 7C illustrate top views of metal oxide layers as a function of an amount of processing time. In some examples, the processing time may refer to an electrochemical oxidation process. The amount of time in which a metal part (e.g., titanium, etc.) is processed may control the texture of the surface of the metal oxide layer - e.g., the metal oxide layer 206 - that overlays a metal substrate. Generally, the roughness of the external surface increases rapidly during the first few minutes of process (e.g., 2 - 10 minutes, etc.), and then more slowly as the thickness of the metal oxide layer increases. Typically, a ∼ 5 - 20 µm thickness of the metal oxide layer will yield interfacial roughness on a 1 - 3 µm scale.
FIG. 7A illustrates an exemplary top view of a metal oxide layer of a metal part exposed to an electrochemical oxidation process for about 2 minutes. The metal oxide layer has an (S_q) value of ∼ 0.33 µm.
FIG. 7B illustrates an exemplary top view of a metal oxide layer of a metal part exposed to an electrochemical oxidation process for about 4 minutes. The metal oxide layer has an (S_q) value of ∼ 0.63 µm.
FIG. 7C illustrates an exemplary top view of a metal oxide layer of a metal part exposed to an electrochemical oxidation process for about 7 minutes. The metal oxide layer has an (S_q) value of ∼ 0.66 µm.
The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Claims

An enclosure for a portable electronic device, the enclosure comprising:
a titanium substrate including a textured surface having peaks separated by valleys, wherein the textured surface has an Sq (root mean square height) that is greater than 0.3 micrometers.
The enclosure of claim 1, wherein tops of the peaks are separated from bottoms of the valleys by a separation distance of 3 micrometers or greater.
The enclosure of claim 1, wherein the textured surface has a gloss value that is less than 1 gloss unit as measured at 20 degrees by a gloss meter.
The enclosure of claim 3, wherein the textured surface has a gloss value that is less than 2 gloss units as measured at 60 degrees by the gloss meter.
The enclosure of claim 4, wherein the textured surface has a gloss value that is less than 10 gloss units as measured at 85 degrees by the gloss meter.
The enclosure of claim 1, further comprising:
a coating that overlays the textured surface, wherein the coating includes dye particles.
The enclosure of claim 1, wherein the textured surface has an Sdq (root mean square gradient) between 0.2 micrometers to 0.5 micrometers.
The enclosure of claim 1, further comprising:
a physical vapor deposition coating that overlays the titanium substrate.
The enclosure of claim 1, wherein the titanium substrate has a Vickers hardness of 350 HV or greater.
A method for forming an enclosure for a portable electronic device, the enclosure including a metal substrate, the method comprising:
forming a metal oxide layer that overlays a surface of the metal substrate by exposing the metal substrate to an electrochemical oxidation process, wherein the surface of the metal substrate is roughened by the electrochemical oxidation process such as to form a texturized surface having alternating peaks and valleys; and

removing the metal oxide layer by applying a stripping solution, thereby revealing the texturized surface of the metal substrate.
The method of claim 10, wherein, prior to forming the metal oxide layer, the method further comprises:
texturizing or polishing the surface of the metal substrate.
The method of claim 10, wherein the stripping solution includes phosphoric acid or sulfuric acid.
The method of claim 10, wherein the metal substrate includes at least one of titanium, hafnium, zirconium, tantalum or niobium.
The method of claim 10, wherein the texturized surface of the metal substrate is unaltered by removing the metal oxide layer.
The method of claim 10, wherein the metal oxide layer includes hemispherical structures that extend from an external surface of the metal oxide layer towards the metal substrate.